Electromagnetic apparatus



Oct. 19, 1943. M. J. FINNEGAN 2,332,139

ELECTROMAGNETIC APPARATUS Filed March 19, 1942 INVENTORL w zfifme Patented Oct. 19,

UNITED STATES PATENT OFFICE 2,332,139 ELECTROMAGNETIC APPARATUS Martin J. Finnegan, Glen Rock, N. 1., asslgnor to Bendix Aviation Corporation, South, Bend, Ind., a corporation of Delaware Application March 19, :1942, Serial No. 435,404 'z-cleims. 01. 175-336) This invention relates to electromagnetic ap paratus, and particularly to the control of theaction of an electromagnetically actuatedrheostat.

InPatent No. 2,268,718, granted to Frederick Newton on January 6, 1942, there is disclosed a rheostat of the carbon pile type, in which the Y carbon pile is subjected to the difierence between two forces of a magnitude large in relation to the pressure needed to vary the pile resistance over its useful range, these forces being derived from the pull of an electromagnet, the excitation of which is dependent on the regulating efiect,

and from an opposing spring.

As is well known, for constant excitation the pull of an electromagnet of usual design upon varies inversely as,

spring or beam which an abutment attached to the electromagnet, with which abutment the spring is brought into .sur-

face contact over a continuously increasing length by movement of the armature towards the electromagnet. As the spring wraps upon the abutment, the length of spring subjected to further bending as the armaturemoves further toward the electromagnet continuously decreases. The spring thus shortens and becomes stifie'r as the length of'the a -gap lessens. Thus basic correspondence with the varying magnet pull results.

In the Newton patent, above ..identified, an attempt at temperature compensation is provided in the form of a spring abutment of bimetallic nature, in which the inclination of the abutment surface varies with temperature, the points of support of the spring moving'in the direction of the' spring pressure and therefore reducing that pressure as the temperature rises.

An object of the present invention is-to. substitute, for the temperature compensating means of the Newton patent, a temperature compensating construction of a novel character, acting to vary the air gap betweenthe armature and fixed parts of the magnetic circuit, rather than to vary the inclination of the spring abutment;

This and other objects of the invention will become apparent from inspection of the following specification when read with reference to the .accompanying drawing wherein is illustrated the preferred embodiment 'of the invention. It is to be expressly understood, however, that the drawing is for the purpose of illustration only, and is not designed as a definition of the limits of the invention, reference being had to the appended claims for this purpose.

In the drawing, reference characters 4, 5, l2, I3, 33, 34, and c designate parts corresponding to parts similarly designated in Fig. 11 of the Newton patent above identified. The bi -metallic coned disc 35, 3 6 of the Newton patent, on the other hand, has been eliminated, so that only 'the single metallic abutment piece 4| appears at the location occupied by such disc 35, 36 in the Newton patent. This abutment 4| fits within the extension 42 of the magnet casing 43, and rests against the annular magnetic 44, the latter being clamped at its periphery by the casing elements 42 and 43.

The carbon pile is made coaxial with the magnet 43 (as in the Newton patent) the carbon washers. I: being assembled upon a porcelain sleeve l3 encasing the armaturespindle 5.

At the outer end the pressure of the pile is taken by a stout carbon washer 3: carried by but insulated from crooked stanchions 34 fixed in a riflange on the magnet body. The stanchions support the pile at a 'sufllcient distance from the electromagnetior the winding of the latter not to be undulyaflected by the relatively high temperature of the pile.

The spring 5| is (as in the Newton patent) a six-rayed plate spring clamped between the armature c and the upper washer 52 by any suit able means (suchas the rivets indicated in Figs. 12 and 13 of the Newton patent) and having its rays engageable with the upper surface of abutment 4|, so as to yieldably oppose the action of the magnetic field upon the armature c, as in the Newton patent.

Instead of varying the inclination of the surface of abutment 4|, to compensate for temperature variations, ,I introduce a novel temperature variation responsive agency in the form-'of-an auxiliary magnetic ring 56 and a bi-metallic washer 51, theformer. being supported by the latter in a position adjacent the main magnetic ring 44 (heretofore describedi'tand being shiftable axially (to reduce the air'g'ap between ring by a rise in temperature due to the heat radiating from magnet winding I. As the outer periphery of washer 51 is confined (although not mechanically clamped) against axial displacement, the major deflection will occur at the inner periphery, and such flexing will shift ring 56 to perature-induced variations in the strength of the magnetic pull.

The disclosed device may form part of the control circuit of an electric motor (as in Fletcher Patent No. 1,971,747) or of an electric generator, as in Fig. 7 of the Newton patent; above identified; or it may be used in other capacities where resistance variation is desirable.

What is claimed is:

1. In an electromagnet, an armature, a fixed core, a winding surrounding said fixed core, a

vary the air gap and thus compensate for tem-,

pair of nested magnetic rings additional to, and

distinct from, said armature and core, and interposed between said winding and said armature, andheat responsive means in contact with said winding for moving one oi said nested rings in relation to the other, to reduce the air gap between said rings and said armature.

2. In an electromagnet, an armature, a fixed core, a winding surrounding said fixed core, a pair of nested magnetic rings additional to, and distinct from, said armature and core, and interposed between said winding and said armature, and-heat responsive means for moving one of said nested rings in relation to the other, to reduce the air gap between said rings and said armature, said heat responsive means comprising a bi-metallic washer interposed between said winding and said rings, said washer having heat absorbing contact with said winding along the major portion of its surface.

MARTIN J. FINNEGAN. 

